Gaseous discharge lamp with a reduced and unreduced actuator



p 1965 M. J. B. THOMAS ETAL 3,274,415

GASEOUS DISCHARGE LAMP WITH A REDUCED AND UNREDUCED ACTUATOR Filed Dec. 31, 1965 United States Patent 3,274,415 GASEOUS DISCHARGE LAMP WITH A REDUCED AND UNREDUCED ACTUATOR Martha J. B. Thomas, Woburn, Mass, and Frank P. Durkee, Derry, N.H., assignors to Sylvania Electric Products Inc, a corporation of Delaware Filed Dec. 31, 1963, Ser. No. 334,767 8 Claims. (Cl. 313-25) This invention relates to mercury lamps, particularly to those known as high pressure mercury vapor lamps.

A typical mercury vapor lamp comprises an inner mercury arc tube supported within an outer jacket coated on its inner wall with a phosphor which absorbs ultraviolet radiation from the arc tube and secondarily emits light in which the arc tube radiation is deficient, for example, red light. Usually the phosphor coating is applied in a lacquer binder which is then baked off. One disadvantage of such lamps is that the lacquer cannot be completely removed by baking and adversely affects the life and light output of the lamp. Another disadvantage is that decline in light output is rapid during early life of the lamp. While some early decline is to be expected, a small reduction in the decline is of significance. Or, stated conversely, an increase of a few percent in the light output maintained through a substantial part of the useful life of the lamp constitutes a valuable advance of the art.

One object of the present invention is to provide a lamp with an improved level of emission characteristics for a substantial part of its life.

Another object is to reduce the harmful effect of residual lacquer and similar impurities in the lamp.

According to the invention a high pressure mercury lamp comprises a mercury arc tube, an outer jacket around said are tube, said outer jacket containing on its inside wall a coating which includes an ultraviolet excitable phosphor and also includes means for supporting said are tube and supplying operating current thereto, at least a part of said coating comprising a phosphate including an unreduced activator, and said outer jacket containing a source of reducing agent in an amount effective to reduce said unreduced activator to activating state and thereby produce additional activated phosphor during operation of the lamp.

For the purpose of illustration a typical embodiment of the invention is shown in the accompanying drawing in which:

FIG. 1 is a side elevation, partly broken away, of a high pressure mercury vapor lamp; and

FIG. 2 is a graph showing relative performance of two mercury vapor lamps.

In FIG. 1, the lamp shown comprises a fluorescent coating 1 on an outer jacket or envelope 2 of light-transmitting material within which an arc tube 4 is supported. The outer envelope 2 is filled with an inert gas such as nitrogen. The are tube 4 is provided with main electrodes 6 and 8 at the ends thereof and an auxiliary electrode 10 disposed adjacent to the main electrode 8. The tube 4 is also provided with a filling of mercury and an inert gas.

The stem press 12 of the outer envelope 2 is provided with a pair of lead wires i=4 and 16, through which the arc tube 4 may be connected to a source of electrical energy. Lead wire 14 is connected to electrode 8 of the arc tube 4 by a metal ribbon 18. A substantially U-shaped support wire is mounted on lead wire 16. Collars 22 and 24, which encircle the arc tube 4 adjacent to the constricted ends thereof, are fixedly attached to the legs of the U-shaped wire 20 and thus support the arc tube Within the outer envelope 20. A plate 26 bridges the free ends of the U-shaped support wire 20 and is fixedly attached thereto to impart rigidity to the structure. The

free ends of the U-shaped support wire 20 are also provided with a pair of resilient metal fingers. 28 which are fixedly attached thereto, the ends of the fingers 28 frictionally engaging the inner wall of the constricted upper end of the envelope 2 to further support the structure. Similarly, the lower portion of the legs of the U-shaped support wire 20 is provided with resilient metal fingers 30 and 32 which are fixedly attached thereto, the ends of the fingers 30 and 32 frictionally engaging the inner wall of the constricted lower end of the envelope 2.

Inside said lower end, a resistor 34 is disposed on wire 20 and is seated on an insulator button 3 5 which, in turn, rests on the upper longitudinal edge of resilient metal finger 32. Lead wire 36 of resistor 34 is wound around support wire 20 and it is also welded thereto. This mode of connection has been found to be particularly advantageous because, even if a weld failure should occur, the tight winding of lead wire 36 about support wire 20 has been found to be adequate enough to maintain the electrical circuit through these members. Lead wire 38 of resistor 34 is welded to metal ribbon 40 which is in turn connected to auxiliary electrode 10 of the arc tube 4.

Although considerable ridigidity is imparted to the structure by positioning the resistor 34 on support wire 20 and winding lead wire 36 of resistor 34 about support wire 20 and welding it thereto, additional structural rigidity may be obtained by positioning the resistor 34 on the support wire 20 so that the lower end thereof is seated on insulator button and the upper end thereof is engaged by a depending flange 42 of collar 24. Another advantage which accrues from the use of insulation button 35 is the elimination of arcing, since the button 35 prevents contact between the body of resistor 34 and support wire 20; this displacement prevents electrolysis of and ultimate arcing through of the resistor core.

Suitable phosphates for the coating 1 include the orthophosphate of an alkaline earth metal such as calcium, strontium or barium, or an orthophosphate of thorium, or a mixture of one or more of these metals with zinc, aluminum, magnesium or cadmium, and an activator such as tin, copper or manganese. As an example, a mixture was prepared of 2.00 moles of calcium hydrogen phosphate, 0.65 mole of calcium carbonate, 0.20 mole of zinc carbonate, 0.02 mole of ammonium chloride and 0.06 mole of stannic oxide. A dry mixture of these ingredients was fired in a porcelain crucible in air for one hour at 1950 F.

Tin, which may have electropositive valence states of 2 and 4, is in its second valence state above ground or metal state in stannic oxide. In the second state it does not activate the phosphate but must be reduced to the first state above ground, as in stannous oxide, which will activate the phosphate. Reduction is accomplished by refiring the dry mixture in an atmosphere of 2% hydrogen and 98% nitrogen for one half hour at 1800 F. This yields an activated phosphor composed of 2 moles of calcium oxide, 0.20 mole of zinc oxide, 1 mole of phosphorus pentoxide and 0.06 mole of stannous oxide as reduced activator.

According to the invention a minor fraction of phosphate containing unreduced activator is mechanically blended with the above described activated phosphor prior to coating it on the inside of the lamp jacket 2. The range of amount of phosphate containing unreduced activator may be 10% to by weight of the total amount of phosphate, reduced and unreduced. Preferably it is 20% to 25%. These proportions of unreduced to total phosphate may be used with other phosphor compositions, such as those described in United States Patent No. 2,901,647. As previously mentioned, other electropositive elements, such as copper, having more than one valence state above ground state, may be used in the 3 higher state, e.g. cupric, as unreduced activator and in the lower state, eg cuprous, as reduced activator.

The phosphate blend containnig both reduced and unreduced activator may be applied as the coating 1 on the inner wall of the outer jacket 2 suspended in a lacquer or organic binder such as ethyl cellulose. The coated wall is then baked at a high temperature below the softening point of the outer jacket until the binder is broken down as completely as possible. Complete break down of the binder is not possible and a residuum comprising a source of reducing agents such as hydrogen and carbon monoxide remains when the outer jacket 2 is sealed by the stem press 12 in a flame. The flame also introduces small amounts of reducing agents in its combustion products within the outer jacket. And further small amounts of reducing agent may be contained within the outer jacket in the form of water and impurities in the glass of the inner and outer jacket, and in the metal supports and leads for the arc tube.

In a typical high pressure mercury vapor lamp the operating temperature within the outer jacket 2 will be 150 to 350 C. At these temperatures the lacquer will further break down and with the other sources of men tioned reducing agents which in turn Will be broken up into reducing species such as atomic hydrogen or carbon monoxide.

According to the invention, instead of harmfully affecting the light output of the lamp, these reducing species are used to reduce the unreduced activator present in the prosphor coating 1. Over approximately the first three hundred hours of operation additional phosphor is thereby activated. Although the very initial light output of the lamp may be lower than that of comparable lamps, the early decline in output is slower and within the first few hundred hours a lamp according to the invention will exceed comparable lamps in light output.

Such a comparison is shown in FIG. 2. Therein the curve A represents the light output in lumens per watt of a 400 watt lamp according to the present invention whose coating comprised a phosphate with tin as reduced activator and as unreduced activator in the ratio of 3 to 1. Curve B represents the light output in lumens per Watt of an identical lamp with the same phosphor except that the activator was 100% reduced tin. The initial light output on curve A was lower (about 62.5 l.p.w.) than on curve B (about 65 l.p.w.). However the output on curve B declined rapidly to about 55 l.p.w. or 85% of its initial value, whereas curve A declined to a higher value of about 57 l.p.w. or 91% of its initial value, between 200 and 300 hours of operation. Thereafter the present lamp maintained its output at the higher level throughout the normal 7000 to 12000 hours of life, it being understood that output is not completely level thereafter but declines very slowly throughout later operation.

From the foregoing description it can be seen that a significant increase in light output is achieved by the present lamp and that the harmful tendencies of impurities are turned to advantage. In addition to an increase in total lumen output, an increase in red light output results from production of additional phosphor making the illumination from the present lamp more natural and useful.

It should be understood that the present invention includes all modifications and equivalents which fall within the scope of the appended claims.

We claim:

1. A high pressure mercury lamp comprising a mercury arc tube, an outer jacket around said are tube, said outer jacket containing on its inside wall a coating which includes an ultraviolet excitable phosphor and means for supporting said are tube and supplying operating current thereto, at least a part of said coating comprising a phosphate and an unreduced activator, and said outer jacket containing a source of reducing agent in an amount eifective to reduce said unreduced activator to activating state 4 and thereby produce additional activated phosphor during opera-tion of the lamp.

2. A high pressure mercury lamp comprising a mercury arc tube, an outer jacket around said are tube, said outer jacket containing on its inside wall a coating which includes an ultraviolet excitable phosphor and means for supporting said are tube and supplying operating current thereto, at least a part of said coating comprising a phosphate and an unreduced activator, and the coating on said outer jacket containing an organic binder residuum as a source of reducing agent in an amount effective to reduce said unreduced activator state and thereby produce additional activated phosphor during operation of the lamp.

3. A high pressure mercury lamp comprising a mercury arc tube, an outer jacket around said are tube, said outer jacket containing on its inside wall a coating which includes an ultraviolet excitable phosphor and means for supporting said are tube and supplying operating current thereto, at least a part of said coating comprising a phosphate including a reduced activator and an unreduced phosphate activator, and said outer jacket containing a source of reducing agent in an amount efiective to reduce said unreduced activator to activating state and thereby produce additional activated phosphor during operation of the lamp.

4. A high pressure mercury lamp according to claim 3 wherein said unreduced activator constitutes 10% to 40% by weight of the total amount of activator.

5. A high pressure mercury lamp comprising a mercury arc tube, an outer jacket around said arc tube, said outer jacket containing on its inside wall a coating which includes an ultraviolet excitable phosphor and means for supporting said are tube and supplying operating current thereto, at least a part of said coating comprising an alkali earth modified phosphate with a reduced and an unreduced activator, and said outer jacket containing a source of reducing agent in an amount etfective to reduce said unreduced activator to activating state and thereby produce additional activated phosphor duping operation of the lamp.

6. A high pressure mercury lamp comprising a mercury arc tube, an outer jacket around said arc tube, said outer acket containing on its inside wall a coating which includes an ultraviolet excitable phosphor and means for supporting said are tube and supplying operating current thereto, at least a part of said coating comprising a phosphate activated by an electropositive element having at least two valence states above ground state, a major fraction of said element being in phosphate activating state, and a minor fraction being in a higher state as unreduced activator, and said outer jacket containing a source of reducing agent in an amount effective to reduce said unreduced activator to activating state and thereby produce additional activated phosphor during operation of the lamp.

7. An alkali earth modified phosphate phosphor activated by an electropositive element having at least two valence states above ground state, a major fraction of said element being in phosphate activating state, and a minor fraction being in a higher valence state as unreduced activator.

8. An alkali earth modified phosphate phosphor activated by an electropositive element selected from the group constituting tin and, copper a major fraction of said element being in phosphate activating state, and a minor fraction being in a higher valence state as unreduced activator of phosphate.

No references cited.

JAMES W. LAWRENCE, Primary Examiner.

C. R. CAMPBELL, Assistant Examiner. 

1. A HIGH PRESSURE MERCURY LAMP COMPRISING A MERCURY ARC TUBE, AN OUTER JACKET AROUND SAID ARC TUBE, SAID OUTER JACKET CONTAINING ON ITS INSIDE WALL A COATING WHICH INCLUDES AN ULTRAVIOLET EXCITABLE PHOSPHOR AND MEANS FOR SUPPORTING SAID ARC TUBE AND SUPPLYING OPERATING CURRENT THERETO, AT LEAST A PART OF SAID COATING COMPRISING A PHOSPHATE AND AN UNREDUCED ACTIVATOR, AND SAID OUTER JACKET CONTAINING A SOURCE OF REDUCING AGENT IN AN AMOUNT EFFECTIVE TO REDUCE SAID UNREDUCED ACTIVATOR TO ACTIVATING STATE AND THEREBY PRODUCE ADDITIONAL ACTIVATED PHOSPHOR DURING OPERATION OF THE LAMP. 